SEOUL, South Korea — South Korea confirmed on Wednesday that it had been in talks with American and North Korean officials about negotiating a peace treaty to formally end the Korean War after more than 60 years, as the United States and its ally try to establish a basis for persuading the North to give up its nuclear weapons.

Chung Eui-yong, the national security adviser to President Moon Jae-in of South Korea, said he had discussed the matter with John R. Bolton, his newly appointed American counterpart, in Washington last week, as they prepared for the planned talks between each of their countries’ presidents and Kim Jong-un, North Korea’s leader. South Korean officials said they had also been in talks with the North about a possible treaty.

Mr. Kim told Mr. Chung and another South Korean official last month that the North was willing to give up nuclear arms if it received security guarantees. In the past, the North has said that a peace treaty and the normalization of ties with the United States would be among the security guarantees it would require in exchange for surrendering its nuclear program.

Referring to his meetings with Trump administration officials, Mr. Chung said on Wednesday, “We held in-depth discussions on various ways of how to end hostilities and eventually establish a peace regime on the Korean Peninsula, how to address the North Korean concerns and how to ensure a bright future for the North if it makes the right choice.”

“Mr. Bolton made it clear to me that he will do his best as an honest broker in successfully implementing President Trump’s peace policy on the Korean Peninsula,” Mr. Chung added.

John R. Bolton, President Trump’s national security adviser, “made it clear to me that he will do his best as an honest broker in successfully implementing President Trump’s peace policy on the Korean Peninsula,” Mr. Chung said.CreditTom Brenner/The New York Times

Treaty Would Have to Involve U.S. and China

The Korean War was halted in 1953 with a truce and has never been formally brought to a close. China fought on the North’s side and the United States on the South’s, and both are signatories to the armistice, along with the North; South Korea, at the time, refused to sign it. Any peace treaty would therefore have to involve Washington and Beijing, South Korean officials acknowledged on Wednesday.

China said on Wednesday that it wanted to play a positive role in formally ending the war, in which an estimated three million Chinese soldiers fought. But it stopped short of endorsing the idea of a treaty, which is likely to involve extensive negotiations and would require the recognition of North Korea by the United States.

“China’s attitude is open and supportive to any peaceful means to resolve the Korean Peninsula issue through consultations,” Hua Chunying, spokeswoman for the Chinese Foreign Ministry, said when asked at a news briefing in Beijing about supporting a possible treaty.

China has promoted the idea of a peace treaty from time to time over the past two decades, to little avail. This time, analysts said on Wednesday, Beijing’s enthusiasm for the idea is likely to be tempered by rising tensions with the Trump administration over trade and Taiwan. Chinese officials are livid over Washington’s move this week to prevent American suppliers from selling parts to the Chinese tech giant ZTE, they said.

“If the two countries cannot settle the trade issues, that will have a significant impact on China’s attitude toward helping the United States on North Korea,” said Cheng Xiaohe, a North Korea expert at the Beijing-based Renmin University. “The ongoing situation with trade is complicating and undermining cooperation.”

At the same time, Mr. Cheng said, China’s relations with North Korea have rapidly warmed in the wake of Kim Jong-un’s surprise visit to Beijing last month. That could give China leverage with North Korea against the United States as Washington works out the terms of the meeting between Mr. Trump and Mr. Kim.

South Korean officials said on Wednesday that they hoped Mr. Kim and Mr. Moon, during their meeting next week, could jointly announce a willingness to denuclearize the Korean Peninsula and ban military hostilities there, as a precursor to a peace treaty.

But Mr. Cheng and other Chinese analysts expressed skepticism that a peace treaty would be signed anytime soon. “If the United States is to sign with North Korea, it needs to do several things,” Mr. Cheng said. “It has to talk to China, and the United States has to recognize North Korea diplomatically.”

Only countries with diplomatic relations can sign a treaty, he said. “A treaty is not a memorandum or a communiqué.”

What the Conditions Might Be

Some analysts in South Korea have suggested that Mr. Moon and Mr. Kim could agree to withdraw weapons and troops from the 2.5-mile-wide Demilitarized Zone, which was created with the armistice and still divides the Koreas. Despite its name, the zone is the world’s most heavily armed border. Although the armistice allows only rifles and pistols within the area, both sides have deployed much heavier weapons and operate guard posts inside the zone.

In the past, the North’s conditions for its denuclearization have included the withdrawal of the 28,500 American troops stationed in South Korea, a demand that Washington and Seoul have adamantly rejected. But Mr. Kim has recently indicated that he could be more flexible about the American military presence in the South if his country no longer felt threatened by it, according to officials and analysts in Seoul.

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South Korean soldiers at the “truce village” of Panmunjom, in the Demilitarized Zone that divides the two Koreas.CreditJung Yeon-Je/Agence France-Presse — Getty Images

“We think that North Korea is more realistic about the security environment on the Korean Peninsula,” Mr. Chung said on Wednesday, referring to Mr. Kim’s decision not to object to recent joint military exercises between South Korea and the United States. The North has typically used such drills as a pretext to conduct weapons tests and reject dialogue.

In 2000, Mr. Kim’s late father and predecessor, Kim Jong-il, told the visiting South Korean president Kim Dae-jung that he could support the American military presence as a peacekeeping force in the region, according to South Korean officials who attended their meeting.

“I am quite sure that if relations between North Korea and the United States improve, the North will not demand the withdrawal of American troops in signing the peace treaty,” Lee Jong-seok, a former South Korean unification minister, said during a forum on Wednesday.

‘There Could Be a Partial Withdrawal’

Formally ending the war would not necessarily mean that Mr. Kim would demand that all American troops be removed, said John Delury, a professor at Yonsei University in Seoul. “There could be a partial withdrawal,” he said. “Remember, all this maneuvering is going on while the United States and South Korea are conducting joint military exercises.”

Still, Mr. Kim seems likely to demand at least a major reduction in troops, said Hugh White, a senior military strategist who worked at the Australian Department of Defense and is now a professor at Australian National University. One outcome, he said, could be a substantial troop withdrawal in exchange for Mr. Kim’s scrapping his intercontinental ballistic missile program.

Such an agreement could appeal to Mr. Trump with his “America First” perspective, Mr. White said. From that point of view, “it could make sense to withdraw from Korea if in return Kim Jong-un scrapped the ICBM program and thus ceased to threaten the continental United States,” he said.

That, Mr. White noted, would transform the American military presence in Asia. “It would be a big win for China,” he said.

Choe Sang-Hun reported from Seoul, and Jane Perlez from Beijing.

A version of this article appears in print on , on Page A10 of the New York edition with the headline: Seoul Confirms Talks on Treaty to End War. Order Reprints | Today’s Paper | Subscribe